/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.iotdb.db.engine.compaction.cross.utils;

import org.apache.iotdb.db.conf.IoTDBDescriptor;
import org.apache.iotdb.db.engine.compaction.cross.AbstractCrossSpaceEstimator;
import org.apache.iotdb.db.engine.storagegroup.TsFileResource;
import org.apache.iotdb.tsfile.file.metadata.ChunkMetadata;
import org.apache.iotdb.tsfile.read.TsFileSequenceReader;
import org.apache.iotdb.tsfile.read.common.Path;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.IOException;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class InplaceCompactionEstimator extends AbstractCrossSpaceEstimator {
    private static final Logger logger = LoggerFactory.getLogger(InplaceCompactionEstimator.class);
    private static final String LOG_FILE_COST = "Memory cost of file {} is {}";

    private boolean tightEstimate;
    private long maxSeqFileCost;

    // the number of timeseries being compacted at the same time
    private final int concurrentSeriesNum =
            IoTDBDescriptor.getInstance().getConfig().getSubCompactionTaskNum();

    /**
     * Total metadata size of each file.
     */
    private final Map<TsFileResource, Long> fileMetaSizeMap = new HashMap<>();

    /**
     * Maximum memory cost of querying a timeseries in each file.
     */
    private final Map<TsFileResource, Long> maxSeriesQueryCostMap = new HashMap<>();

    public InplaceCompactionEstimator() {
        this.tightEstimate = false;
        this.maxSeqFileCost = 0;
    }

    @Override
    public long estimateCrossCompactionMemory(
            List<TsFileResource> seqResources, TsFileResource unseqResource) throws IOException {
        if (tightEstimate) {
            return calculateTightMemoryCost(unseqResource, seqResources);
        } else {
            return calculateLooseMemoryCost(unseqResource, seqResources);
        }
    }

    private long calculateMemoryCost(
            TsFileResource unseqResource,
            List<TsFileResource> seqResources,
            IFileQueryMemMeasurement unseqMeasurement,
            IFileQueryMemMeasurement seqMeasurement)
            throws IOException {
        long cost = 0;
        Long fileCost = unseqMeasurement.measure(unseqResource);
        cost += fileCost;

        for (TsFileResource seqFile : seqResources) {
            fileCost = seqMeasurement.measure(seqFile);
            if (fileCost > maxSeqFileCost) {
                // only one file will be read at the same time, so only the largest one is recorded here
                cost -= maxSeqFileCost;
                cost += fileCost;
                maxSeqFileCost = fileCost;
            }
            // but writing data into a new file may generate the same amount of metadata in memory
            cost += calculateMetadataSize(seqFile);
        }
        return cost;
    }

    private long calculateLooseMemoryCost(
            TsFileResource unseqResource, List<TsFileResource> seqResources) throws IOException {
        return calculateMemoryCost(
                unseqResource, seqResources, TsFileResource::getTsFileSize, this::calculateMetadataSize);
    }

    private long calculateTightMemoryCost(
            TsFileResource unseqResource, List<TsFileResource> seqResources) throws IOException {
        return calculateMemoryCost(
                unseqResource,
                seqResources,
                this::calculateTightUnseqMemoryCost,
                this::calculateTightSeqMemoryCost);
    }

    private long calculateMetadataSize(TsFileResource seqFile) throws IOException {
        Long cost = fileMetaSizeMap.get(seqFile);
        if (cost == null) {
            cost = getFileReader(seqFile).getFileMetadataSize();
            fileMetaSizeMap.put(seqFile, cost);
            logger.debug(LOG_FILE_COST, seqFile, cost);
        }
        return cost;
    }

    private long calculateTightFileMemoryCost(
            TsFileResource seqFile, IFileQueryMemMeasurement measurement) throws IOException {
        Long cost = maxSeriesQueryCostMap.get(seqFile);
        if (cost == null) {
            long[] chunkNums = findTotalAndLargestSeriesChunkNum(seqFile, getFileReader(seqFile));
            long totalChunkNum = chunkNums[0];
            long maxChunkNum = chunkNums[1];
            cost = measurement.measure(seqFile) * maxChunkNum / totalChunkNum;
            maxSeriesQueryCostMap.put(seqFile, cost);
            logger.debug(LOG_FILE_COST, seqFile, cost);
        }
        return cost;
    }

    // this method traverses all ChunkMetadata to find out which series has the most chunks and uses
    // its proportion to all series to get a maximum estimation
    private long calculateTightSeqMemoryCost(TsFileResource seqFile) throws IOException {
        long singleSeriesCost = calculateTightFileMemoryCost(seqFile, this::calculateMetadataSize);
        long multiSeriesCost = concurrentSeriesNum * singleSeriesCost;
        long maxCost = calculateMetadataSize(seqFile);
        return Math.min(multiSeriesCost, maxCost);
    }

    // this method traverses all ChunkMetadata to find out which series has the most chunks and uses
    // its proportion among all series to get a maximum estimation
    private long calculateTightUnseqMemoryCost(TsFileResource unseqFile) throws IOException {
        long singleSeriesCost = calculateTightFileMemoryCost(unseqFile, TsFileResource::getTsFileSize);
        long multiSeriesCost = concurrentSeriesNum * singleSeriesCost;
        long maxCost = unseqFile.getTsFileSize();
        return Math.min(multiSeriesCost, maxCost);
    }

    // returns totalChunkNum of a file and the max number of chunks of a series
    private long[] findTotalAndLargestSeriesChunkNum(
            TsFileResource tsFileResource, TsFileSequenceReader sequenceReader) throws IOException {
        long totalChunkNum = 0;
        long maxChunkNum = Long.MIN_VALUE;
        List<Path> paths = sequenceReader.getAllPaths();

        for (Path path : paths) {
            List<ChunkMetadata> chunkMetadataList = sequenceReader.getChunkMetadataList(path, true);
            totalChunkNum += chunkMetadataList.size();
            maxChunkNum = chunkMetadataList.size() > maxChunkNum ? chunkMetadataList.size() : maxChunkNum;
        }
        logger.debug(
                "In file {}, total chunk num {}, series max chunk num {}",
                tsFileResource,
                totalChunkNum,
                maxChunkNum);
        return new long[]{totalChunkNum, maxChunkNum};
    }

    public void setTightEstimate(boolean tightEstimate) {
        this.tightEstimate = tightEstimate;
    }
}
